Process for degassing liquids

ABSTRACT

Process and apparatus for degassing liquids, namely water, with mobile and stationary application, according to the principle of underpressure generation by suctioning a portion of the liquid from the chamber, which, after the degassing, is filled automatically again with gas-containing liquid, whereupon the next degassing cycle occurs.

BACKGROUND OF THE INVENTION

The invention relates to a process for degassing liquids in closedsystems by applying a pressure which is lower compared to the systempressure.

PRIOR ART

In removing gases from liquids, primarily from water, one generallydifferentiates between

1. removing (venting) excess gases which exceed the specific solutionequilibrium,

2. driving out (degassing) chemically dissolved gases.

1.) Gases comprised in excess in water generally present considerableproblems in circulating systems (heating systems, cooling systems,air-conditioning systems). As extremely fine air bubbles, they generateflow noises, cavitation and erosion in the materials and degrade theuniform heat transport in the pipe network and on the surfaces providedfor the heat exchange, such as coolers and heating surfaces.

To avoid these problems, ventilation equipment is produced whichoperates generally with a stop valve disposed in a chamber and connectedwith a float. When the chamber is filled, the rising float closes thevalve. Conversely, the float opens the valve when air enters thechamber. Such ventilation devices are frequently air collection pots,cyclone pots or vessels with massive bodies which are intended for theextremely fine air bubbles to combine into larger ones in order to risesubsequently in the chamber of the ventilator.

2.) If greater gas volumes are comprised in the water than are necessaryfor chemical saturation, this quantity represents a feeding reservoir toreestablish the natural saturation concentration which is lost, forexample, through the reaction of a gas with the materials in thesolution. In order to drive out the excess gas and also the gasescomprised in the solution, thermal degassing equipment is beingmanufactured in which, on the one hand, by increasing the temperature,the gas solubility is reduced and, on the other hand, the expulsioneffect is enhanced thereby that steam is forced through the water to bedegassed and the resulting steam bubbles entrain the gas particles inthe water and carry them outside to the outside atmosphere.

Other devices generate a reduced pressure above the level of the liquidwhereupon the gases also escape to the surface.

DISADVANTAGES OF PRIOR ART

Regarding 1.)

According to Henry's law, ventilation devices can only remove thosequantities of gas which are greater than the factors temperature,pressure and medium properties permit in terms of solubility. Inprinciple, in a circulating system two different pressure regions alwaysobtain between intake and pressure region of a circulation pump suchthat in theory a ventilator disposed on the intake side of a pump shouldtransport gas out of the system. But in practice, narrow limits are setbecause the ventilator must be under minimum pressure so that its floatchamber remains filled. Otherwise the float drops and opens theventilation valve such that air can be drawn in via the ventilator (theventilator becomes an aerator).

But if a minimum pressure is required on the low-pressure side, the aircan only be incompletely removed. A further disadvantage of this type ofventilation is that, due to the high flow rate of the water, themicrobubbles can only reach the float chamber of the ventilator in smallquantities if at all.

Regarding 2.)

According to Henry's gas law, as expanded by Dalton, the partialpressure acting upon a solution, the temperature and the type of mediumdetermine the solubility of gases. With the known technique of thermaldegassing, extremely good results can be attained in this regard. Amarked disadvantage of this technique, however, is that it requireslarge and expensive equipment: a steam generator for producing theexpulsion steam and a collecting vessel with degasser device comprisinglarge distributor surfaces on which the water can be exposed to thesteam. Part of this equipment includes extensive tubing, regulatingelements, control means and the safety technique of steam operation.Such thermal degasser installations are a fixed standard component insteam generation installations.

In closed cooling water circuits, heating or cooling water circulations,they are neither economically nor practically applicable since thedegassed water would have to be heated and subsequently cooled again tothe circulation temperature.

The problem is similar in so-called fast steam generators in which arelatively small system water quantity is present and for which athermal degassing installation would be too large.

SUMMARY OF THE INVENTION

Required is a cost-effective apparatus for mobile and stationaryapplication, with which excess gas, as well as also the chemicallydissolved gases, can be removed from a liquid (for example water). Itshould not be necessary to raise the temperature of the liquid to bedegassed and the apparatus should be operable in a simple manner andrequire low energy for its operation.

Solution

The task is solved according to the invention thereby that from a watersystem a portion of the water is extracted and transferred to thedegassing container of the described apparatus. By extracting a portionof the liquid and transporting it to a storage container the totalpressure (and thus the partial pressures on all gases) is lowered in thedegassing container so far that the boiling point of the liquid isexceeded and the liquid boils. The solution equilibrium of the dissolvedgases shifts toward the left and as a consequence all excess gases aredriven out with the steam bubbles. The temperature of the liquid is notraised.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention and other objectsrelating thereto, reference will be made to the following detaileddescription of the invention which is to be read in association with theaccompanying drawings wherein:

FIG. 1 is a schematic representation of the degassing apparatus of thepresent invention;

FIG. 1a illustrates the flow path of fluids in the apparatus shown inFIG. 1 when the apparatus is in a circulation mode;

FIG. 1b illustrates the flow path of fluid when the apparatus is in anevacuation mode; and

FIG. 2 illustrates a further embodiment of the invention.

DESCRIPTION OF THE INVENTION

The invention relates to a process for degassing liquids under lowpressure with the associated equipment either connected in parallel withthe circulation system or, in batch operation, from a first containerwith gas-containing liquid a specific quantity is extracted, degassedand transferred to a second closed container.

FIG. 1 shows such a degassing apparatus. By means of a pump (3) from acirculation (1) via a line segment (2) liquid is removed, pumped via ajet pump (4) and an automatic valve (5) through a container (6) and fromthere is transferred via a jet pump (7) and line segments (14), (8) andthe automatic valve (23) back into the circulation (1). The automaticvalves (11) and (12) are closed. A circulation is generated in thecourse of which through the container (6) gas-containing circulatingwater is flushed. The jet pump (4) empties the diaphragm pressurestorage (21) completely and recycles the liquid stored there back intothe circulating cycle. The circulation time can be set to be of anydesired length via a timer clock (9).

At the end of the circulation time the timer clock (10) starts theevacuation time. Automatic valves (11) and (12) are opened and automaticvalves (5), (23) are closed. The liquid is now pumped in a cycle by pump(3) via the line segment (13) through the automatic valve (11) andthrough the jet pump (7), further via line segments (14) and (15)through the automatic valve (12). In the jet pump (7) a strong currentis generated such that on the intake side of the jet pump (7) a verystrong underpressure is generated. In this way the liquid is drawn fromthe container (6) and forced with the circulation flow via line segments(14), (15), (13) into the partial line segment (16) and subsequentlythrough the jet pump (4) into the diaphragm storage (21). The size ofthe diaphragm storage (21) and its gas supply pressure are calculatedand determined according to the liquid quantity equal to the evacuationquantity to be displaced. Depending on the setting of the underpressureand the liquid temperature, the liquid starts to boil spontaneously incontainer (6). The driven-out gases rise into the upper pipe outlet (17)of container (6) and further into the float chamber of the ventilator(18). At this point in time they are not yet capable of escaping intothe atmosphere via the check valve (19) since in the container (6)underpressure still obtains. After the expiration of the evacuation timeset on the timer clock (10), the circulation time starts again on thetimer clock (9). The functions performed during the circulation timehave already been described above. During the circulation the container(6) is again filled completely and the system pressure is exerted ontoit. All steam bubbles condense and the gases driven out collect in thepipe outlet (17) as well as in the ventilator (18). The liquid levelrises into the ventilator (18) and forces the gases through theventilator (18) and the check valve (19) to the outside. A manometer(20) has two functions. It indicates the excess pressure as well as alsothe underpressure during the operating cycles ‘circulation’ and‘evacuation’.

FIG. 1a shows the flow paths in the degassing apparatus in the switchedstate ‘circulation’, i.e. charging the apparatus with gas-containingcirculating water. During the circulation the check valve (22) preventsa shortcircuit between the water inlet and the water outlet of the maincirculation.

FIG. 1b depicts the flow paths in the degassing apparatus in theswitched state ‘evacuation’, i.e. of the degassing of the liquid presentin container (6).

FIG. 2 shows an apparatus functionally identical with FIGS. 1, 1 a and 1b, however, additionally equipped with a device for collecting andrecycling of condensate, as well as with an additional device forreplenishing the volume loss, generated during the degassing, with anequal quantity of water.

DESCRIPTION

Basic settings of the valves with the installation switched off beforestarting operation:

Manual valves 81, 82, 84, 86 are open.

Manual valves 79, 80, 83, 85, 87, 88 are closed.

Automatic valves 60, 61, 62, 63, 64, 65, 66, 67 are closed

Preparing installation for operation:

The installation is filled via the replenishment line segment 54. Forthis purpose a switch 95 is set to “off”, and switches 94 and 96 areswitched to “on”. If switch 96 is switched to “on”, the automatic valve66 opens and the replenishment water can flow into the installation tothe extent the pressure reducer valve 90 is opened.

The installation is now filled via the replenishment line segment 54.The air escapes via the exhaust line segment 55. The filling process iscompleted when no air escapes via the pipe line segment and themanometers 104, 106, 105 and 107 indicate identical pressure.

During the filling process the pressure reducer valve 90 is presettoward the end of the fill time to the system pressure obtaining at theinlet point 30. Subsequently the manual valves 79 and 80 are opened.Thereby within the degasser installation and the water system to bedegassed an identical pressure develops.

By adjusting the restoring pressure on the pressure reducer valve 90 thefinal system pressure can be corrected during the degassing.

The supply pressures of the diaphragm expansion vessels (MAG) 112 and113 are set with the installation switched on (main switch 94 to “on”)and the pump switched on (switch 95 to “on”) on the manometer 107 areset to the pressure obtaining during the time of the transfer by pumping(timer 68).

To set the supply pressure in the MAGs, the manual valves 86 and 84 areclosed, subsequently the manual valves 85 and 87 are opened until theMAGs are empty of water. Subsequently the valves are closed again andthe gas supply pressure is set in the MAGs by means of nitrogen gas tothe previously read-off display of the manometer 107. The installationis now ready to start and the vacuum degassing can start:

Timertime1=Timer 68: transfer by pumping, exchange of water content.

Switch 95 switches on pump 40. Subsequently the program flow is reset bybriefly switching on/off the switch 94.

A pump 40 draws water from a water system via the junction point 30 andthe pipe line segment 48, passing through a dirt trap 31 and a checkvalve 32, transports it via the pipe line segment 49 into the vacuumvessel or closed container 34 further via the pipe line segment 50 andthe junction point 38 back into the water system. The automatic valves60, 61, 62, 65, 66 are opened for this purpose; 63, 64, 67 remainclosed. During the transfer process by pumping, through the jet pump 42via the pipe line segment 53 the MAG 112 is emptied completely bysuction provided it was not completely emptied during the precedingoperating step (see below). The pressure on the manometer 102 falls tothe supply pressure set in the MAG. In this way it is possible to checkwhether or not the supply pressure of the MAG 122 is still correct. Thetime of the transfer by pumping is determined by setting the timer 68 inthe control switchboard 76. The transfer quantity is counted by thecontact water meter 33. It transmits 11 pulses which are indicated onthe control switchboard 76 through light 72. In this way it is possibleto determine via the time setting on timer 68 the transfer quantity(exchange quantity).

Timertime2=timer 69: suctioning vacuum

At the completion of time 68 the switch positions of the automaticvalves change:

Valves 60, 63, 64 are open.

Valves 61, 62, 65, 66, 67 are closed.

Valve 67 can open. Explanations in this regard are explained below.

A fast internal circulation develops in the pipe line segment 51 withthe direction pump 40>automatic valve 63, jet pump 41>automatic valve 64such that on the intake side of the jet pump and the pipe line segment58 a strong underpressure is generated and water is suctioned out of thevacuum vessel. Thereby at the output of pump 40 a high pressure isgenerated through which the suctioned water is forced into the MAG 112through line segment 49, the jet pump 42 (now without effect) and theline segment 53. The display on manometer 102 rises.

Via pipe line segment 52 it is ensured that after the automatic valve 65a very low pressure obtains such that the valve always closes optimallyand, in the presence of a vacuum, no water can flow via the pipe linesegment 48 into the installation. With a vacuum present, the exhaustline segment 55 is closed via the check valve 44, the condensate linesegment 56 via the automatic valve 67 and the outlet line segment viathe check valve 35.

The display on the manometer 107 falls to underpressure. Analogously,the display on the manometer 102 rises. An upper pressure limitation isset on the pressure regulator 97 such that upon reaching an undesirablyhigh pressure the installation switches off automatically and the alarmlight 75 lights up. The process of vacuum suction can be observed viathe inspection pipe 36, if the manual valves 81 and 82 are open.

If the condensate collection vessel 46 is filled at the beginning of thevacuum suction, i.e. the magnet float 100 of the probe rod 101 is at theupper reed switch 98, the automatic valve 67 opens and the condensate issuctioned back into the installation until the magnet float has reachedthe lower reed switch 99. During times 68 (transfer by pumping) and 71(pressure equilibration) the valve 67 cannot open. A residual quantityof condensate remaining after the passage of time 70 (maintainingvacuum) must, if necessary, wait for the next cycle to be suctionedback.

Timertime3=Timer 70: maintaining vacuum

After completion of time 69, the automatic valve 60 is closed. The valvesettings at this time are:

Valves 63, 64 are open.

Valves 60, 61, 62, 65, 66, 67 are closed.

Valve 67 can open if the condensate vessel 46 is full (see above).

The internal circulation in the pipe line segment 51 remains extant butno more water is suctioned from the vacuum vessel 34 so that a restingtime occurs in which all gas and steam bubbles can rise into the upperregion of the vacuum vessel 34 and into the air collection chamber 43.The rise can be observed on the inspection pipe and it is possible todetermine in this way the length of the time 70 which must be set.During this time the internal pressure falls as a function of the watertemperature and can be read off on the manometer 107.

Timertime4=Timer 71: internal pressure equilibration

At the expiration of time 70 the automatic valve 61 is opened. The valvesettings are at this time:

Valves 61, 63, 64 are open.

Valves 60, 62, 65, 66, 67 are closed.

The internal circulation in pipe line segment 51 remains extant.Simultaneously, the water stored in MAG 112 flows via the pipe linesegments 53 and 59 into the vacuum vessel 34 such that within the closedinstallation the pressures can become equilibrated as much as possible.

The cycle starts anew.

Timertime1=Timer 68: transferring by pumping, exchanging water content.

The functions performed in this time have already been described above.

After the installation has completed the times 69=vacuum suctioning,70=maintaining vacuum, 71=internal pressure equilibration and thetransfer time 68 has started anew, through the changed valve position(see above) the vacuum is spontaneously broken so that water vaporformed also spontaneously condenses with the consequence that with valve66 open in the replenishment line segment 54 the volume deficitgenerated through the degassing is replaced by replenishment water untilthe system pressure has reached the pressure set on the pressure reducervalve. Simultaneously, the driven-out gas and a residue of non-condensedwater vapor escapes (at last under system pressure) via the exhaust linesegment 55 into the condensate collection vessel 46. There line 55 isintroduced so deeply that its end is below the residual water level withthe result that exiting water vapor can better condense there.

Different apparatus embodiments of the process are possible. Forexample, the liquid extraction for the purpose of evacuation can takeplace directly by means of a suction pump or with the aid of a pistonmoving in the downward direction in a cylinder. The principle of theprocess is the same, which is the reason for omitting a graphicrepresentation of it at this point.

Attainable Advantages

With the apparatus according to the invention degassing capacities canbe achieved which come close to the effect of a thermal degasser. If theissue is driving out oxygen for the purpose of corrosion prevention, theremaining residual quantity of oxygen can usually be tolerated. For theresidual corrosion avoidance in special cases either an oxygen-bindingchemical product can be added or a corrosion preventive agent whichtolerates the presence of oxygen. Since chemical oxygen binders, such asfor example sodium sulfite NaSO₃, such as are conventionally used forcorrosion protection, simultaneously place loading on the system withadditional salts, the dangerous oversalting of circulations with, forexample, sodium sulfate NaSO₄ occurs. The same applies to fast steamgenerators in which significant quantities of sodium sulfite are usedfor the purpose of oxygen binding.

By driving out oxygen, considerable quantities of water chemicals can besaved in such water, which free the waste water of the loading.

Applications

Initialization and redevelopment heating systems, cooling water andair-conditioning circulations, degassing of feed water in steamgenerators, in particular fast steam generators, for stand-down timeconservation of steam boilers, degassing of fire protection pipe systems(sprinkler installations) and other applications.

LIST OF REFERENCE NUMBERS ON FIG. 2

30 inlet

31 dirt trap

32 check valve line segment 48

33 contact water counter

34 vacuum vessel

35 check valve line segment 50

36 inspection pipe

37 37

38 outlet

39 39

40 pump

41 vacuum pump 1

42 vacuum pump 2

43 air collection chamber

44 check valve line segment 56 exhaust

45 exhaust valve actuated via float

46 condensate collection vessel

47 check valve line segment 58 suctioning back condensate

48 pipe line segment system water suctioning

49 pipe line segment 1 forcing water into the installation

50 pipe line segment water outlet

51 pipe line segment internal circulation

52 pipe line segment vacuum augmentation

53 pipe line segment MAG1 charging-emptying

54 pipe line segment replenishment fresh water

55 pipe line segment ventilating

56 pipe line segment suctioning back condensate

57 pipe line segment manual filling condensate vessel

58 pipe line segment vacuum suctioning

59 pipe line segment 2 forcing water into the installation

60 MV pump at pressure side

61 MV vacuum vessel input

62 MV vacuum vessel+system output

63 MV jet pump input

64 MV jet pump output

65 MV system+pump input

66 MV fresh water replenishment

67 MV condensate recycling

68 timer transferring by pumping, filling

69 timer suctioning vacuum

70 timer maintaining vacuum

71 timer pressure equilibration

72 light circulation

73 light pump

74 light replenishment

75 light excess pressure

76 control switchboard

77 77

78 78

79 HV system input

80 HV system output

81 FV inspection pipe top

82 HV inspection pipe bottom

83 HV installation emptying

84 HV MAG1 inflow+outflow

85 HV MAG 1 emptying

86 HV replenishment fresh water

87 HV MAG2 emptying

88 HV filling condensate vessel manually

89 89

90 pressure reducer

91 check valve

92 92

93 93

94 switch main

95 switch pump on/off

96 switch replenishment water automatic/manual

97 switch, off, excess pressure

98 reed switch vessel full

99 reed switch vessel empty

100 float with magnet

101 probe rod with 2 reed switches

102 manometer MAG1 actual pressure

103 manometer MAG2 actual pressure

104 manometer degasser input

105 manometer degasser output

106 manometer fresh water after pressure reducer

107 manometer vacuum vessel+pressure

108 108

109 109

110 110

111 111

112 MAG1 water take-up+release

113 MAG2 replenishment after vacuum

114 114

115 115

What is claimed is:
 1. Apparatus for degassing a liquid in a closedsystem that includes: a vertically disposed closable container forholding a quantity of liquid, said container having a top and a bottom,a circulating loop for liquid containing a circulation pump, an inletline for bringing liquid from said supply into the circulating loop,said inlet line containing an inlet control valve, an outlet line forreturning liquid from said circulating loop back to the supply, saidoutlet line containing an outlet control valve, a supply line forconnecting the circulating loop with the top of said container, saidsupply line containing a supply control valve which, when open, allowsthe container to be filled with liquid, a first jet pump for connectingthe bottom of said container and said circulating loop, a second jetpump for connecting the supply line to an intermediate diaphragmpressure tank, and control means for closing the control vales andactuating the jet pump so that liquid is drawn from the container anddelivered into the pressure tank during a degassing cycle whereby anunder pressure is produced in the tank sufficient to release gases fromthe liquid into the top of said tank.
 2. The apparatus of claim 1 thatfurther includes ventilator means in the top of said tank for exhaustinggases from said tank.
 3. The apparatus of claim 1 that further includesa circulating control valve mounted in said loop, one valve beinglocated between the inlet and outlet liner and the other valve beinglocated between the circulating pump and said first jet pump.
 4. Theapparatus of claim 1 that includes means for returning the liquid insaid pressure tank to the system upon the completion of a degassingcycle.
 5. The apparatus of claim 1 wherein said control means furtherincludes means for replenishing the volume of liquid lost during eachdegassing cycle.
 6. A method of degassing a liquid drawn from the closedsystem, closing the container to the surrounding ambient, using a jetpump and a circulation pump to withdraw a portion in the container sothat an under pressure is created in the container such that gases insaid liquid escape from said liquid and are collected above said liquidin the top of said container, storing the liquid withdrawn from thecontainer within at least one intermediate pressure tank at about thepressure of said closed system, and evacuating the gases from saidcontainer.
 7. The method of claim 6 that includes the further step ofmixing the liquid stored in the intermediate pressure tank with theliquid in the closed supply at the end of a degassing cycle and adding aportion of the stored liquid to the liquid in the container at the startof a subsequent degassing cycle.